This invention refers to a fat-removing labyrinth filter for aspirating hoods.
The filtration of fatty particles in suspension in the air flow of a ventilator placed inside a kitchen aspirating hood is of particular relevance for the following reasons.
In the first place, because the filtration keeps the inside of the hood cleaner, thus preventing the deposition of fat which may under certain circumstances constitute a fire risk, and in the second place because it significantly minimizes the need for periodical maintenance and cleaning operations.
The filtration of such fatty particles extends the lifetime of the internal component parts of the hood, such as the motor, the wiring, the switches, the lamp holders, the lamps and the rubber or plastic elements, by preventing the strong corrosive and decomposing attack of the fatty acids.
It also allows an optimum use of odor preventing hoods based on activated charcoal and of internally re-circulating hoods, by preventing their rapid saturation caused by fatty particles penetrating the pore spaces of the activated charcoal.
Finally, the filtration of the fatty particles allows keeping clean the ducts discharging air to the outside, and to prevent pollution.
It is therefore understandable that a lot of attention has been dedicated to these problems by the manufacturers of both filters and hoods, and that a variety of solutions have been advanced by them.
The fat-removing hoods known to this date can essentially be classified into the following categories.
In the first place, the filters based on synthetic fiber pads of 10-20 mm thickness, which are low cost but present the following disadvantages: a low to medium head loss, a low to medium efficiency of not over 50%, an high risk of fire due to an excess of retained acids in case of little or wrong maintenance, a need to be cleaned by hand in a long and fastidious process, a duration limited to a few months, a need for repurchasing at a not insignificant periodical expense, and a troublesome installing operation.
A second class of known filters is based on synthetic fiber pads of a thickness of 1-2 mm, which are low-cost but have a low to medium head loss, an average efficiency not exceeding 60%, a limited but definite fire risk and a lesser accumulation of fats even in case of limited maintenance.
Finally, they cannot be cleaned and need replacement, with the consequent periodical purchasing expense and corresponding replacement operations. Their lifetime is also limited to a few months.
Other known filters are based on multiple-layer metallic filters made of stretched metal plate, generally of aluminum. These are characterized by high efficiency in the range of 90%, no fire hazard, low to medium head-loss and compact size.
These filters also constitute a highly effective barrier against any external flames or flames originating from the cooking range; they can also be cleaned in dishwashing machines, easily disassembled and reassembled and present a high durability, even if washed frequently.
However, they present a high cost and an outer appearance which is pleasant but related to the finishing of aluminum, generally of an anodized type, which is poorly suitable for combining with stainless steel, copper and brass.
An additional known class is constituted by metallic labyrinth filters, made of alternating metal profiles, in particular made of stainless steel.
The main characteristics of labyrinth filters is in that the air flow charged with fatty particles is suddenly changed in direction more than across a labyrinth made of communicating spaces formed by guiding surfaces, whose geometry may be designed in various ways and with different degrees of deviation. These sudden changes result in a deposition of part of the fatty particles on the guiding surfaces, because of their difficulty of changing direction because of their weight, which is much heavier than air.
Every deviation provokes the deposition of parts of the fatty particles, which may, after a few deviations, reach a loss of efficiency close to 90%. The labyrinth filter must be periodically cleaned, by hand or in a dishwashing machine, by operations of a greater or lesser simplicity depending on their production type, and their lifetime is generally unlimited. For all these models, the rule of a total recovery of their functional and esthetic efficiency after a washing operation applies.
However, in the metallic labyrinth filters normally available on the market the efficiency of fat particle separation is generally achieved by providing a generous sizing and therefore a broadening of the surfaces touched by the flow, rather than a high number of diramations; it follows that these filters are quite heavy and exhibit a considerable thickness in the range from 29 to 35 mm, which makes it impossible to insert them into the products of a simple and compact design in accordance with the growing modern trends.
Such filters constitute a generally high thickness barrier, from 20.35 mm, and are consequently a heavy obstacle in producing compact units.
This considerable thickness is indispensable to provide labyrinthine passages adequately sized to provide filtration efficiency and limited head losses.
Moreover, while offering an esthetic appearance more in line with that of stainless steel, these filters are rather massive and heavy because of their few large ribs, a fact that prevents them from being slim, modern appliances.
The purpose of this invention is therefore to produce a fat-removing labyrinth filter for aspirating hoods having a high efficiency despite being housed in an extremely compact enclosure.
Other purposes of the invention are to produce a fat-removing filter for aspirating hoods so as to be lightweight, readily cleaned even in dishwashing machines, easily disassembled and reassembled, and endowed with an unlimited lifetime without presenting any fire hazard.
A further purpose of the present invention is to produce a filter of a cost essentially lined-up with the cost of multi-layered aluminum filters, and therefore not very expensive.
Further characteristics of the invention are defined in the claims attached to this patent application.